Bring ziploc freezer bags just in case you need to hold random doodads or snacks. Depending on where you are going, you may not be allowed to take fresh fruit off the ship. We had boxes of cereal, cookies, chips, etc., from the dining room on hand to tide the kids over if they got hungry between mealtimes while we were off the ship.
Bring more than one bathing suit per person if you think you'll be spending a lot of time at the beach/pool. You can wear one while the other dries.
Earplugs and a sleeping mask. You don't know who your neighbors will be, and there are lots of random blinking lights that you wouldn't expect in those cabins.
If you have walkie talkies, they are a great way to keep in touch while people do their own thing on the big boat. Sometimes cell phone coverage is spotty.
Stamps if you think you'll want to send (domestic) postcards.
I have often wished I brought a book light when I have to share a room with other people.
We didn't need a surge protector or lanyards on our cruise.
Have a great time!